Defending against Resource Exhaustion

When dealing with denial of service via resource exhaustion, you are faced with two problems: how to detect the attack (before your system goes catatonic, that is), and how to react.

XXX: draft only

• Resource metering (network rate limiting, memory consumption, number of processes)

• Choose proper limits.

• You can also use dynamic resource limits based on system load. Current system load is available through the function getloadavg on BSD and on Linux systems.

• Set hard resource limits as a last resort. If you exceed one of these limits, your application will receive a signal and exits. This is a condition that a functioning system can deal with gracefully (e.g. by restarting the service with a clean slate). The only way to deal with a wedged system is manual intervention (usually by hitting the red button and keeping your fingers crossed that the file system check will go through).